Note: There are some known issues with CU6 RTM concerning Hybrid environments and when used in co-existence with Exhange 2007. Please check this post for updates.

Today, Cumulative Update 6 for Exchange Server 2013 was released by the Exchange Team (KB2936880). This update raises Exchange 2013 version number to 15.0.995.29.

This Cumulative Update increases the Public Folder for Exchange On-Premises to 100,000. It also fixes the ‘Hybrid Configuration Wizard ‘Subtask Checkprereqs Execution Failed’ issue I blogged about here (2988229).

This Cumulative Update contains the following fixes:

• 2991934 Duplicate mailbox folders after migration to Exchange Server 2013
• 2983512 RPC Client Access service crashes on an on-premises Mailbox server in an Exchange Server 2013 hybrid environment
• 2983426 AutodiscoverSelfTestProbe fails when external URL is not set for EWS virtual directory in Exchange Server 2013
• 2983423 AutodiscoverSelfTestProbe fails when external URL is not set for ECP virtual directory in Exchange Server 2013
• 2983422 The ServerWideOffline component is set to Inactive after Exchange Server 2013 prerequisite check fails
• 2983207 “532 5.3.2” NDR when you send an email message to a hidden mailbox in an Exchange Server 2013 environment
• 2983066 Removed Default or Anonymous permission for Outlook folders cannot be restored in an Exchange Server 2013 environment
• 2982769 “Topology service cannot find the OWA service” when you perform an eDiscovery search in Exchange Server 2013
• 2982763 Mail-enabled public folder accepts email messages from unauthorized users in an Exchange Server 2013 environment
• 2982762 OAB generation arbitration mailbox can be removed or disabled in an Exchange Server 2013 environment
• 2982760 The Enter key submits duplicate sign-in forms to Outlook Web App in an Exchange Server 2013 environment
• 2982759 You cannot access the archive mailbox of a delegated user after enabling MAPI over HTTP
• 2982017 Incorrect voice mail message duration in an Exchange Server 2013 environment
• 2981835 You cannot add attachments, delete or move many email messages in bulk in Outlook Web App
• 2981466 MAPI/CDO client cannot connect to Exchange Server 2013
• 2977279 You cannot disable journaling for protected voice mail in an Exchange Server 2013 environment
• 2975599 Exchange Server 2010 public folder replication fails in an Exchange Server 2013 environment
• 2975003 Calendar item body disappears in Outlook online mode in an Exchange Server 2013 environment
• 2974339 OAB generation fails if FIPS is used in an Exchange Server 2013 environment
• 2971270 Blank page after you sign in to Exchange Server 2013 EAC (formerly ECP)
• 2970040 Folder Assistant rule does not work correctly in an Exchange Server 2013 environment
• 2965689 EAS device cannot sync free/busy status if an item is created by EWS in an Exchange Server 2013 environment
• 2963590 Message routing latency if IPv6 is enabled in Exchange Server 2013
• 2961715 “Something went wrong” error in Outlook Web App may show an incorrect date
• 2958434 Users cannot access mailboxes in OWA or EAS when mailbox database is removed

Notes:

• There are some additional changes in the way Public Folders operate. Consult this article from the Exchange team for details on these changes.
• When using Exchange hybrid deployments or Exchange Online Archiving (EOA), you are required to keep up to date.
• Be advised of OAB architectural changes introduced with CU5 which are documented here. If you are affected, it is recommended to update CAS servers prior to Mailbox servers.
• If you have installed the Interim Update to fix Hybrid Configuration Wizard, you can install the Cumulative Update over it – there is no need to uninstall the IU prior to installing CU6.

This Cumulative Update includes schema and AD changes, so make sure you run PrepareSchema / PrepareAD. After updating, the schema version will be 15303.

Note that Cumulative Updates can be installed directly, i.e. no need to install RTM or Service Packs prior to installing Cumulative Updates. Note that once installed, you can’t uninstall a Cumulative Update nor any of the installed Exchange server roles. The order of upgrading servers is irrelevant, unlike with previous generations of Exchange.

Finally, and I can’t emphasize this enough: For any Hotfix, Rollup, Service Pack or Cumulative Update, I’d recommend to thoroughly test this in a test and acceptance environment first, prior to implementing it in production. When you lack such facilities, hold out a week or two and monitor the comments on the release article or TechNet forum for any issues.

You can download Exchange 2013 Cumulative Update 6 here; UM Language Packs can be found here. More details about these changes, preparing Active Directory or installing this Cumulative Update can be found in the original announcement.